<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //...展开 针对可以迭代，可遍历的对象
        var arr = [2,3,4];
        var b = [5,6,7];
        var res = arr.concat(b);
        console.log(res)
        arr.push(...b);//=arr.push(5,6,7)
        console.log(arr)
    </script>
</body>
</html>